As a general trend, a glass material for use in sealing is used for sealing of various kinds of electronic products which are used with the inside thereof being kept in a high vacuum and for sealing of electronic component packages for preventing entering of corrosive gas or moisture in order to ensure the operation stability. This glass material for use in sealing is made of low-melting glass powder, and a glass continuous layer having glass powder fused thereon is formed by pasting the powder with organic binder solution, coating a sealed portion of an article to be sealed with the pasted powder and burning the article in an electric furnace or the like to strip a vehicle ingredient.
Conventionally, mainly lead glass powder of PbO—B2O3 series is widely used as such a glass material for use in sealing. That is, lead glass having a low melting point and ease of melting of PbO can be used for sealing at a low processing temperature and within a wide temperature range, and lead glass having low thermal expansion, superior adhesion, superior adherence, superior chemical stability and the like provides advantages of high sealing property, high sealing strength and high durability.
However, since lead is a toxic substance, there is an occupational safety and health problem in a manufacturing step of lead glass, and there is a concern about how to deal with disposal of electronic components or electronic products, since disposal of untreated electronic components or electronic products at the end of life usefulness for which lead glass was used for sealing could cause soil contamination or groundwater contamination due to lead being eluted by acid rain or the like and disposal by landfill or the like is prohibited under recent strict environmental regulations while limited application due to inclusion of lead makes recycling difficult.
Suggested measures for such problems are: to use low-leaded glass including Pb of 10-23% for a stem mount or the like for sealing a glass valve (Japanese Unexamined Patent Publication No. 8-180837); and to provide a groove for preventing entry of etchant at a front plate and a back plate of a plasma display panel on the inner side of a marginal lead glass sealing portion, dip the plasma display panel at the end of life usefulness into etchant to remove lead glass of a sealing material selectively and repair a deteriorated portion for recycling (Japanese Unexamined Patent Publication No. 2000-113820). However, fundamental measures cannot be obtained since toxic lead is still included in the waste product even though the amount of lead can be decreased by using low-leaded glass as in the former method. Moreover, with the latter method of removing the lead glass sealing portion by etching, the amount of labor and costs required for the removing process causes a decrease in the advantage of recycling, and the method also has a cost disadvantage in a manufacturing stage due to formation of the groove.
Against this background, development of a glass material for use in sealing of lead-free series which can substitute a conventional general-purpose lead glass series has been strongly demanded. Therefore, the present inventors have already suggested lead-free glass materials for use in sealing of B2O3—ZnO—BaO series and of V2O5—ZnO—BaO series (Japanese Unexamined Patent Application No. 2001-391252) and a lead-free glass material for use in sealing of V2O5—ZnO—BaO—TeO2 series (Japanese Unexamined Patent Application No. 2003-041695). These glass materials for use in sealing are of lead-free series, can be used for sealing at a low processing temperature and within a wide temperature range, have low thermal expansion coefficients, are superior in adhesion, sealing processability, adherence, chemical stability, strength and the like and comprise practical performance which can sufficiently substitute lead glass in a glass composition having a material oxide set within a specific ratio range.
Although the lead-free glass materials for use in sealing according to the above suggestions by the present inventors comprise superior practical performance as described above, it should be understood that development of a sealing material which offers higher performance in the range of choices for the material to be sealed, the sealing processability and the sealing quality is still desired.